Y-TZP ball heads were introduced into the market in 1985. Since then these components have had wide diffusion in hip replacements, due to their good mechanical performance and reliability. Namely, only a few papers were published up to year 2000 reporting failures of Y-TZP ball heads. The worldwide recall in August 2001 of some Y-TZP batches changed this situation. This paper analyse the material of a ceramic ball head that fractured in vivo 34 months after surgery. The retrieved fragments were submitted for visual inspection, fractographic analysis by optical microscopy, X-ray diffractometry, and FEG-SEM ceramography analysis. The results obtained show that the hydrothermal stability of the material had only a secondary role in the fracture. The literature reporting on failures of THR making use of Y-TZP ball heads is discussed.

We studied factors contributing to the initiation of fracture and failure of a zirconia ceramic femoral head. The materials retrieved during a revision total hip replacement were submitted to either visual, stereomicroscopic and scanning electron microscopy (SEM) or SEM and energy-dispersive X-ray analysis. X-ray diffraction was performed in order to investigate the extent of tetragonal to monoclinic phase transition. Histological examination was performed on the periprosthetic tissues. The results showed that failure was due to the propagation during clinical use of defects which may have been introduced into the material during the processing of the ceramic, rather than those intrinsic to zirconia. The literature relating to previous failures of zirconia components is reviewed.

We studied factors contributing to the initiation of fracture and failure of a zirconia ceramic femoral head. The materials retrieved during a revision total hip replacement were submitted to either visual, stereomicroscopic and scanning electron microscopy (SEM) or SEM and energy-dispersive x-ray analysis. X-ray diffraction was performed in order to investigate the extent of tetragonal to monoclinic phase transition. Histological examination was performed on the periprosthetic tissues. The results showed that failure was due to the propagation during clinical use of defects which may have been introduced into the material during the processing of the ceramic, rather than those intrinsic to zirconia. The literature relating to previous failures of zirconia components is reviewed.

For the last 30 years Alumina and Zirconia ceramics constituted the ceramic materials used for the manufacturing of Total Joint Arthroplasty, thanks to the high biological and mechanical properties of these materials (Piconi and al, 2003; Piconi and Maccauro 1999). The new ceramic biocomposite ZPTA (Alumina Matrix Composites by Transformation Toughened and in situ Plateled Reinforcement) that is currently known as Biolox® delta, produced by CeramTec (namely ZPTA in the paper), improving the mechanical properties when compared to Alumina (Burger W. and Richter H.G. 2000), allowed to manufacture components which were not previously possible, and especially the small- diameter ball heads (<28 mm), thin-walled cup insert, knee and finger joints. Few paper reported the in vitro and in vivo biocompatibility tests on this new material (Willmann, et al. 2000), and in particular as ceramic joints are intended for use in younger patient (Black 1997, Schmalzried 2001), hence the ones with longer life expectations, the study of the chronic effects of small particles, in term of local and systemic toxicity, including carcinogenesys becomes more and more relevant (Archimbeck et al. 2000).

Wear is the main limiting factor to artroprostheses’ lifetime: at local level the cascade of events induced by reactions to wear debris is still the most frequent cause of implant failure and revision, while the ions released by wear debris originate systemic reactions, depending on their transport by the blood flow to peripheral organs, thanks to the vascularization of the reactive membrane surrounding the implant. (Schmalzried and Callaghan 1999, Urban et al. 2000, Archimbeck et al. 2000, Fisher et al 2001, Sedel 2001, Dumbleton et al. 2002).

Tetragonal zirconia polycrystal (TZP) is a new interesting ceramic for the manufacture of medical devices. Its wide use in orthopedic and odontoiatric implants was limited till now by the high chemical and radiochemical impurities of the raw materials. Purification processes now available allow to obtain high purity ceramic grade powders suitable for TZP ceramics manufacture, even if their possible mutagenic and transforming effects are still unclear. The aim of this work is to study in vitro the mutagenic and oncogenic effects of a new zirconia ceramic stabilized by yttria (Y-TZP). This ceramic was sintered from high purity powders obtained by a process developed under a project carried out within the Brite EuRam programme. For comparison, ceramics made from unpurified zirconia powder were also tested. Fibroblasts irradiated by a linear accelerator were used as positive control. The results obtained show that Y-TZP ceramic does not elicit either mutagenic or transforming effect on C3H/10T1/2 (10T1/2) cells and demonstrate that ceramic from high purity powders can be considered suitable for biomedical applications from the point of view of the effects of its radioactive impurity content.

Due to their excellent mechanical properties, Yttria-stabilized Tetragonal Zirconia Polycrystal ceramics (Y-TZP) are used in ball heads for Total Hip Replacements. It is known that Y-TZP materials may show strength degradation due to ageing or to hydrothermal treatment. Also high wear of UHMWPE sockets coupled to steam sterilized Y-TZP ball heads after a short implantation period was recently reported. This effect may be related to ball head surface phase transformation, due to corrosive attack. The aim of this study is the evaluation of Y-TZP ceramics stability. Y-TZP made out of Yttria coated powders were aged at 140°C under 0.2MPa water pressure, in Ringer’s solution at 37°C, in NZW rabbits. Samples made out Yttria coated powders show lower strength degradation than samples made out coprecipitated powders, and UHMWPE discs coupled to Y-TZP rings made out coated powders do not show increase in wear after repeated sterilization cycles of the ceramic rings.

There is interest in using zirconia for biomedical applications as ballheads for total hip prostheses. Two potential types are under discussion:partially stabilized zirconia (PSZ) and tetragonal zirconia polycrystals (TZP)materials. Because of its enhanced material properties, TZP stabilized withyttria is favourable. To eliminate high amounts of natural radioactiveimpurities, the precursors are purified. The kind of precursor and purificationmethod determine the powder impurity level. The disadvantage of Y-TZP is thatthe hydrothermal decomposition reaction method is that it depends very stronglyon the grain size and the distribution of the stabilizing yttria within thezirconia grains. Thermodynamical and kinetic investigations on high puritycoprecipitated and yttria-coated zirconia powders show different behaviours.Y-TZP materials based on yttria-coated zirconia powders show excellentmechanical strength of more than 1000 MPa, a Weibull modulus of up to 20 a!nd a fracture toughness of 9 MPa√m. The material properties of Y-TZP ceramicsbased on coprecipitated powders and prepared under the same conditions are lessattractive. It is expected that materials based on yttria-coated zirconia willshow enhanced properties compared to materials derived from coprecipitatedpowders. Therefore Y-TZP materials derived from yttria-coated powders are veryattractive as medical grade zirconia.

The strength of specimens made of different zirconia qualitities and of alumina were determined in dependence on hydrothermal treatment and on loading rate. The load bearing capacity of hip joint heads made of zirconia were measured using different taper qualities. It is shown that the strength properties measured under standard environmental conditions must not be regarded as the only decisive criterion for choosing an appropriate ball head materials.

There is interest in zirconia being used in biomedical applications as ball heads for total hip prostheses. Two potential types are under discussion: partially stabilized zirconia (PSZ) and tetragonal zirconia polycrystals (TZP) materials. Because of its enhanced material properties especially TZP stabilized with yttria is favourable. To eliminate high amounts of natural radioactive impurities, the precursors are purified. It depends on the kind of the precursor and the purification method to achieve powders having a very low impurity level. Thermodynamical and kinetic investigations on high purity coprecipitated and yttria coated zirconia powders show a different behaviour.